First, check that none of the 4WD control buttons are stuck in or halfway in. With the H3 on, try cycling through the different modes. But often this might be an ABS sensor issue, anything from mud in the tone ring to a failed sensor to a damaged lead wire. I had this coming on last month on and off for a couple of weeks and it went away. I was about to buy new rear ABS sensors as my first troubleshooting step since the front ones are pretty new.
But if the left front tire isn't actually low (drive it for a bit to turn on the TPS, they go to sleep when stopped) then the first troubleshooting step is always the H3 battery, connectors and cables when there are mysterious issues related to anything electrical.
As I think about it, ABS is the more likely issue between the 4WD buttons vs. ABS. If it's the 4WD buttons and/or encoder motor, usually you'd only get the Service 4WD message.